In order to transport plural substrates used for a display panel or the like at one time, a substrate transport device as shown in FIG. 27 is commonly employed. The transport device shown in FIG. 27 is constituted by a packing material 201 having a rectangular vertical hole 203, which is made of foam polypropylene or the like. Further, the transport device is formed in a rectangular column (square column) having a bottom, and is provided with ribs 205 on an inner wall of the vertical hole 203. The number of the ribs 205 is one less than the number of substrates to be stored. With the ribs 205, the vertical hole 203 is partitioned and grooves 204 are formed. The number of the grooves 204 is equal to that of the substrates. Further, each of the grooves 204 receives a substrate 202 fitting in so that the substrate 202 is stored. By transporting a set of the substrates stored in such a manner, it is possible to transport the plural substrates at one time.
Further, the Japanese Unexamined Patent Publication, No. 287382/1998 (Tokukaihei 10-287382, publication date: Oct. 27, 1998) discloses an arrangement in which a substrate is loaded on a substrate carrying tray, and which allows plural substrate carrying trays to be stacked one upon another. In the publication, Tokukaihei 10-287382, the substrate carrying tray has a frame on its four edges, the frame having four side surfaces extending in a vertical direction. Further, the frame has four corners on which concave portions are provided so that part of each concave portion has an offset in parallel with each of the side surfaces. Further, in a vertical downward direction from the parts on which the concave portions are provided, convex portions are provided that can fit in the concave portions, respectively. With the above structure, when plural substrate carrying trays are stacked, the convex portions of a substrate carrying tray stacked above fit in concave portions of a substrate carrying tray positioned below. This enables plural substrate carrying trays to be stacked.
However, in such a substrate transport device in which each substrate is stored in a groove of the vertical hole, every substrate is held by ribs 205 only at its edge portion, and no other portions including its center portion are supported. This has caused a fear that, when a substrate is used for a large size display panel, the substrate is warped and the center portion of the substrate contacts the center portion of another substrate, resulting in breakage of the substrate.
Further, the substrate carrying tray described in the publication, Tokukaihei 10-287382, is required to have an elbow room between an outer side surface of every concave portion and an inner side surface of every convex portion, considering manufacturing errors and fitting adjustability. If no elbow room is provided, the following may occur in the case where a substrate carrying tray stacked above is made larger than a substrate carrying tray positioned below. Specifically, the upper substrate carrying tray cannot be fit in the lower substrate carrying tray, so as to run on to the lower substrate carrying tray.
However, providing such an elbow room causes another problem when trays are stacked in multiple levels, e.g. 30 levels. Specifically, when plural substrate carrying trays are stacked, the trays may be slightly inclined leftward or rightward when viewed from a side direction. This causes trays, stacked in multiple levels including levels inclined leftward and levels inclined rightward, to have a waveform as a whole or to have inclination made leftward (or rightward). Thus, stability cannot be attained in the stacked condition.
The present invention is made in view of the foregoing problems, and an object of the present invention is to realize a substrate carrying tray which eliminates a fear of breakage of a substrate when the substrate is warped and contacts another substrate, and which can be stacked stably.